1. Field of the Invention
The present invention relates to a voltage detecting device for a camera.
2. Description of the Prior Art
Conventional voltage detecting devices for a camera have power supplied to an electromagnetic member which controls the start of the running of a leader screen and a follower screen of a shutter curtain or, to an electric load which is equivalent to the electromagnetic member just before a release operation, in order to detect the power source voltage so that it can be judged as to whether or not a normal release operation is possible. When it is judged that a release operation is not possible, by detection of the power source voltage, the release operation is inhibited, thus preventing the problem of the shutter curtain being left open.
However, in the case of a long time release or a bulb release, it takes a long period of time from the moment that the power source voltage is detected (just before the release operation), until the moment when the power is actually supplied to the electromagnetic member for controlling the start of the running of the follower screen. Therefore it is difficult to judge, from the value of the power source voltage detected before the release, whether or not the running of the follower screen is possible. That is, especially at the time of a bulb release, the photographer is to determine at will, the length of time from the running of the leader screen until the running of the follower screen. However, sometimes the shutter is left open for as long as half a day. Thus it is very difficult to judge from detection of the voltage before the release, at what level of the power source voltage the release operation becomes impossible. Therefore, it becomes necessary to set the reference voltage at a considerably high level in order to judge whether or not the release operation is possible (guaranteed) by the power source voltage before the release, which then generates the problem of the battery life becoming short. Also, in this kind of system, for a bulb release in which the release time can be set at any desired length of time, a voltage level which can guarantee the running of the follower screen for that chosen length of time, in principle, cannot be set. Also, even if the voltage level is set at a considerably high level, the problem of the shutter being left opened as a result of the follower screen being unable to run, cannot be solved.
Also, heretofore, there has been a system in which control of the running of the leader screen is done by supplying power to an electromagnetic member for the leader screen, while contrary thereto, control of the running of the follower screen is accomplished, by the release of the power supply to an electromagnetic member for the follower screen. It has been proposed that in this system, the state in which power is supplied to the electomagnetic member, for control of the running of the follower screen when the shutter is opened after the running of the leader screen, is utilized for detecting the power source voltage at the time when power is supplied thereto. However, a basic problem in such a system is that since the follower screen is retained by supplying power to the electromagnetic member, power consumption will be great as in the case of a long time release or a bulb release, thus the life of the battery is shortened considerably.
An object of the present invention is to provide a voltage detecting device for a camera in which an exact judgement can be made as to whether or not a release operation is possible in spite of any shutter time length that is chosen by the photographer, and at the same time the life of the battery can be extended.
Other objects of the present invention shall be clarified by the following detailed explanations thereof.